1. Field of the Invention
The present invention relates to a heat-sensitive recording material and more particularly to a heat-sensitive recording material of high sensitivity which can be stored in a high-temperature environment with substantially no reduction in the whiteness of white area (unrecorded area) on the recording material and without adhesion of residual substances to the thermal head.
2. Prior Art
Heat-sensitive recording materials are well known which make use of the color forming reaction of a colorless or pale-colored basic dye with a color developing material such that the two materials are brought into contact with each other by heating to produce a color image.
Since the above heat-sensitive recording materials are relatively inexpensive, and record images are formed thereon with use of a compact recording device with an easy maintenance, the recording materials are widely used for various applications. With the diversity of applications, these recording materials have been more frequently stored in high-temperature environments, as in a storehouse in summer time or in the storeroom of a ship cruising on the sea in the tropical zone. Because of a need for inexpensive miniaturized recording devices, new type recording devices are currently available which do not have ventilating means that are almost always provided in conventional recording devices, and which are equipped with most simplified power source possible. However, the new type recording devices have drawbacks due to these features. The heat-sensitive recording material stored as rolled in, e.g., an energized small-size facsimile device is invariably exposed to the heat generated from the power source to develop undesired color at least in part, thereby easily becoming impaired in the whiteness of the background white area. Due to the miniaturization of power source, a reduced amount of energy is applied for recording so that record images of high density can not be produced using conventional color developing system. In addition, an increased amount of residual substances such as a basic dye, color developing material, heat-fusible material and other additives fused in the recording layer are piled up on the thermal head since the recording proceeds before the viscosity of fused materials sufficiently decreases.